1. Field of the Invention
The present invention relates to heat curable silicone rubber seal and gasket materials and, specifically, such a material containing hollow microspheres.
2. Description of the Prior Art
Silicone compositions were produced commercially as early as the late 1930's and early 1940's. The unique physical properties of silicone, such as its thermal resistance and dielectric properties, made silicone compositions well suited for numerous applications. Early uses for silicone compositions included electrical insulating applications and greases for military use. One class of silicone compositions, silicone elastomers or rubbers, are recognized for their outstanding ability to resist change at elevated temperature and exposure to adverse weather conditions over extended periods of time. Silicone rubbers have today evolved to become very versatile elastomers with the estimated annual silicone usage in the United States having grown to over 50 million pounds.
Because of their special properties, silicone rubbers have mainly been used in the past in applications at extremely high or low temperatures. Typical uses are wire and cable insulation, seals and gaskets for aircraft, and seals for electric and electronic equipment. They are effective in an approximate range of minus 50.degree. F. to 450.degree. F.-500.degree. F.
Because of their special characteristics, silicone rubbers have not, in general, been widely used to form more typical seals such as those found in lighting fixtures, window seals, oven door seals, or oil seals.
A need exists for a composition and method of producing a silicone rubber seal or gasket which utilizes commercially available materials and which can be carried out economically with a minimum of extra manufacturing steps and without requiring highly controlled process conditions.
A need exists for a silicone rubber seal suitable for use in lighting gaskets, window seals, oven door seals, and oil seals which exhibits reduced permeability against gasses, water vapor, oil and other contaminants. A need exists for such a seal with an improved compression set where the seal material is used to join interfitting components and where the components are torqued down in sealing relationship.